A communication system is operable to communicate information between a sending station and a receiving station by way of a communication channel. A radio communication system is a communication system in which the communication channel by which information is communicated between the sending and receiving stations is formed upon a portion of the electromagnetic spectrum. Such a communication channel is sometimes referred to as a radio channel. Because a radio channel does not require a wireline connection for its formation, a radio communication system inherently permits an increase in communication mobility relative to communication systems which require wired connections to form a communication channel.
Bandwidth limitations, which limit the communication capacity of many types of communication systems, are particularly acute in radio communication systems. Such bandwidth limitations in a radio communication system are typically due to limitations on the amount of the electromagnetic spectrum allocable to the radio communication system. Such bandwidth limitation limits the increase of communication capacity of a radio communication system. Increase of the communication capacity of the system, therefore, is sometimes only possible by increasing the efficiency by which the allocated spectrum is used. Other types of communication systems similarly can exhibit a communication capacity increase as a result of increase in the efficiency by which the communication channels formed between sending and receiving stations of such systems are utilized.
Digital communication techniques, for instance, provide a manner by which to increase the efficiency by which to effectuate communications upon communication channels of a communication system. Implementation of digital communication techniques in a radio communication system is particularly advantageous due to the particular needs to efficiently utilize the spectrum allocated to such a system.
Information which is to be communicated in a communication system utilizing digital communication techniques is typically digitized into discrete, digital bits. Groups of the digital bits are sometimes formatted into packets to form packets of data. The packets of data are communicated by the sending station, either individually or in groups, at discrete intervals to a receiving station. Once received at the receiving station, the packets of data are concatenated together to recreate the informational content contained therein. A packet of data shall herein refer both to a request packet as well as an information packet.
In some of such communication systems, when a packet of data is received at a receiving station, the receiving station returns an acknowledgment to the sending station to indicate whether the packet of data has been successfully communicated to the receiving station. If the packet of data is indicated not to have been successfully communicated, the packet is retransmitted.
Because packets of data can be communicated at discrete intervals, the communication channel upon which the packet is transmitted need not be dedicated to a single sending-receiving station pair. Instead, a shared communication channel can be used to communicate packets of data communicated between a plurality of sending-receiving station pairs. Because of the shared nature of the shared channel, improved communication capacity is possible.
Sometimes the shared channel is formed of a random access channel in which sending stations are permitted random access thereto to communicate a packet of data thereon. While permitting the random access to the shared channel to transmit packets of data thereon provides a simple manner by which to effectuate communication of packets of data, lack of coordination between separate sending stations of separate-receiving station pairs might result in collisions of packets of data. That is to say, separate sending stations might attempt to transmit separate packets of data during overlapping time periods. Typically, when a collision condition occurs, the packets of data interfere with one another to an extent to prevent the recreation of their information content subsequent to reception at receiving stations.
Packet data communications are effectuated, for instance, in conventional LANs (local area networks). Wireless networks operable in manners analogous to wired LANs have also been developed and are utilized to communicate packets of data over a radio link upon which a random access channel is defined. A High Performance Local Area Network type 2 (HIPERLAN/2) standard promulgated by the ETSI BRAN (Broadband Radio Access Network) project sets forth a standard of operation of an exemplary wireless LAN. Mobile terminals operable therein transmit packet data upon random access channels to an access point of the infrastructure of the wireless LAN. When a packet of data is successfully communicated to the access point, a feedback acknowledgment indicating the successful communication is returned to the mobile terminal. And, if a collision or other error condition occurs, a feedback acknowledgment indicating unsuccessful transmission of the packet is returned to the mobile terminal.
In the just-mentioned BRAN system, as well as in other packet data communication systems, if a packet of data is not successfully communicated to a receiving station, the packet is retransmitted, typically according to a retransmission scheme. For instance, back-off schemes, such as a binary exponential back-off scheme, have been implemented to minimize the occurrence of collisions by exploiting the feedback acknowledgments returned by the receiving station. Back-off schemes generally provide an improved manner of effectuating retransmission of packets of data from sending stations. An exemplary back-off scheme is described in the IEEE 802.11 standard.
Conventional exponential back-off schemes, such as the scheme set forth in the IEEE 802.11 standard, is predicated on various assumptions, including immediate feedback. Also, conventional, exponential back-off schemes have been intended for statically-defined systems. That is to say, conventional back-off schemes have generally been applied to systems in which the frame formats by which the packets are communicated are unchanging.
In a typical back-off scheme, a contention window is defined. The contention window has boundaries and the packet of data is transmitted upon a channel within the contention window boundaries. If the packet is not successfully communicated, the size of the contention window is increased and the packet is retransmitted.
The aforementioned BRAN system, as well as others, include a dynamic slot allocation (DSA) scheme in which random access channels allocated to a particular frame are dynamically allocated. Successive frames might have different allocations of random access channels.
Advantage is not taken of the variable nature of random access channels assigned in a dynamic slot allocation system, such as that proposed for the BRAN system in existing exponential back-off schemes.
A manner by which to define the size of a contention window utilized in a back-off scheme which takes into account the dynamic nature of a DSA system and which is better operable in a delayed feedback system would, therefore, be advantageous.
It is in light of this background information related to the communication of packet data that the significant improvements of the present invention have evolved.